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CaesarsCipher.js
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/*
Caesars Cipher
One of the simplest and most widely known ciphers is a Caesar cipher, also known as a shift cipher. In a shift cipher the meanings of the letters are shifted by some set amount.
A common modern use is the ROT13 cipher, where the values of the letters are shifted by 13 places. Thus 'A' ↔ 'N', 'B' ↔ 'O' and so on.
Write a function which takes a ROT13 encoded string as input and returns a decoded string.
All letters will be uppercase. Do not transform any non-alphabetic character (i.e. spaces, punctuation), but do pass them on.
Remember to use Read-Search-Ask if you get stuck. Try to pair program. Write your own code.
Here are some helpful links:
String.prototype.charCodeAt()
String.fromCharCode()
*/
function rot13(str) { // LBH QVQ VG!
function shift13(charVal) {
// we're only concerned with uppercase letters
var shiftVal = 13; // Can reuse
if (charVal >= 78) {
return String.fromCharCode(charVal - shiftVal); // since ROT13 is reciprocal, change direction
} else if (charVal <= 64) {
return String.fromCharCode(charVal);
}
return String.fromCharCode(charVal + shiftVal);
}
var shiftedStr = "";
for (var i = 0; i < str.length; i++) {
shiftedStr += shift13(str.charCodeAt(i));
console.log(shiftedStr);
}
return shiftedStr;
}
// Change the inputs below to test
rot13("GUR DHVPX OEBJA QBT WHZCRQ BIRE GUR YNML SBK.");